Diesel engines may use re-ingested burnt exhaust gases to increase fuel economy and reduce emissions. For example, an exhaust gas recirculation (EGR) system may be used to recirculate exhaust gases from the exhaust manifold to the intake manifold. Such operation can displace fresh air and lower oxygen concentration in the cylinder, as well as reduce formation of NOx during combustion.
In some engine configurations that have a turbocharger, both a low pressure and high pressure EGR system may be used. For example, a high pressure (HP) EGR loop from the exhaust manifold (upstream of the turbine of turbocharger) to the intake manifold (downstream of the compressor of the turbocharger), may be used. In addition, a low pressure (LP) loop from downstream of the turbine to upstream of the compressor may also be used. See, for example, U.S. Pat. No. 6,820,599.
The inventors herein have recognized several disadvantages with such an approach. Specifically, in some engine configurations, a mass airflow (MAF) sensor may be installed to estimate or measure flows in the HP EGR and LP EGR loops. However, over time, the sensor may degrade or age, thus reducing the ability to accurately control the HP and/or LP EGR. Further, when both EGR systems are active, a reading from the MAF sensor can be biased because interactions between the two EGR systems. As such, degraded estimation, and thus control, of the HP and LP EGR systems can result.
At least some of the above issues may be addressed by a system for a diesel engine having an intake manifold and an exhaust manifold, comprising: a turbocharger between the intake and exhaust manifolds of the engine; a low pressure exhaust gas recirculation system with a first end coupled to the exhaust manifold downstream of the turbocharger and a second end couple to the intake manifold upstream of the turbocharger, said low pressure exhaust gas recirculation having a first valve coupled thereto for regulating flow; a high pressure exhaust gas recirculation system with a first end coupled to the exhaust manifold upstream of the turbocharger and a second end coupled to the intake manifold downstream of the turbocharger, said high pressure exhaust gas recirculation having a second valve coupled thereto for regulating flow; a first mass airflow sensor coupled in the engine intake manifold upstream of said second end of said low pressure exhaust gas recirculation system; and a control system configured to diagnose the degradation of said first mass airflow sensor. In this way, it is possible to identify degraded operation of the sensor and take corrective action, if necessary.
Several different diagnostic strategies can be used to detect the degradation of the MAF sensor. In one particular example, the diagnostic strategy of the MAF sensor may be based on information from a second MAF sensor. In another example, an intrusive strategy may be used where system operation is purposely adjusted to enable improved diagnosis of the MAF sensor under selected conditions. In yet another example, conditions may be opportunistically identified under which improved diagnostics may be performed, such as when a low pressure EGR valve is closed, for example.
In this way, the degradation of a MAF sensor can be diagnosed so that the control of dual EGR system may be monitored to improve robustness and/or durability.
In another embodiment, the disclosed approaches can make it possible to detect leakages or blockages of the low pressure EGR loop, and thus degradation of an EGR system can be provided.
In yet another example, a control system can provided which adapts to degradation of a MAF sensor, such as an aging effect. In this way, the EGR flows in the dual EGR system can be more accurately controlled even in the presence of sensor degradation. Thus, it is possible to provide robust control of both EGR systems by providing accurate estimation of EGR flow via adaptation of degraded MAF sensor performance.